1. Field of the Invention
This invention relates to line sensors employed in apparatus of the type having a line sensor for scanning an image in one direction and means for displacing the image relative to the sensor in a direction perpendicular to the line scan to effect a raster scan of the image, and more particularly to a color sensitive line sensor for use in such scanning apparatus.
2. Discussion Related to the Problem
Apparatus for scanning motion picture film to produce a television signal is well known. Usually, in such film scanning apparatus, a film frame is scanned in a direction generally perpendicular to the length of the film at a standard television field rate. In the past, the line scan has been accomplished by flying spot scanners employing Nipkow discs, movable reflecting elements or cathode ray tubes. The use of a solid-state line sensing array as an alternative to a flying spot scanner to provide the line scanning function in a film scanner has been proposed, See. D. T. Wright, "Solid-State Sensors; The Use of a Single Dimension 512-Element Array for Film Scanning", BBC Research Department Report No. 1973/32. The potential advantages of a line sensing array over a flying spot scanner are numerous, including: reduced size, weight, maintenance and cost. These advantages make the solid-state line sensing array particularly attractive for use in a film scanner for displaying amateur movie film on a home television set. The ability to scan color film to produce a color television signal would be a very desirable feature in such a film scanner.
It has been suggested (see I. Childs and J. R. Sanders, "An Experimental Telecine Using a Line-Array CCD Sensor", SMPTE Journal, Vol. 87, No. 4, April 1978), that color operation could be achieved by employing a conventional prism block beam splitter, of the type used in color TV cameras, in combination with three line sensing arrays to provide the three color separation signals. The advantages of this approach are the rather complex optical system required to split the beams and the precision mechanical adjustment required to register the separate sensors.
An alternative approach, based on analogy with prior art solid-state image sensing arrays, would be to mask individual photosites along a single line sensor with a pattern of color filters such as R, G, B, R, G . . . . The output video signal would then be demultiplexed into three channels, each channel having samples of only one color. The signal samples in the channels could then be interpolated to supply continuous R, G and B color separation signals. This technique would obviate the need for beam splitters and precision mechanical registration but would suffer from reduced resolution. In addition, the process of filter fabrication for individual photosensing sites is difficult, and the light absorbed by a filter over one color photosite is unavailable to another photosite of the same picture element group, thereby reducing the light gathering efficiency of the sensor.
The problem therefore is to provide a color image sensor configuration that does not require the precision mechanical alignment and complex optical beam splitting arrangement of the three sensor configuration, yet is free from the precision filter manufacturing requirements and limited resolution of the color filter array sensor configuration.